Related Party Transactions - Narrative (Details) - USD ($) $ in Millions					3 Months Ended		9 Months Ended		15 Months Ended
		Jun. 15, 2019	Jun. 14, 2019	Dec. 20, 2018	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Asset coverage per ratio					178.00%		178.00%		178.00%	184.00%
Incentive fees waived	[1]				$ 15	$ 15	$ 45	$ 15
FS/KKR Advisor, LLC
Related Party Transaction [Line Items]
Incentive fees waived quarterly									$ 15
FS/KKR Advisor, LLC | Investment Advisory Agreement
Related Party Transaction [Line Items]
Management and service fees, base rate		1.00%	1.50%	1.50%
Asset coverage per ratio		150.00%	200.00%
Incentive fee (in percent)		17.50%	20.00%				20.00%
Incentive fees waived quarterly									15
Incentive fees waived									90
FS/KKR Advisor, LLC | Affiliated Purchaser Program
Related Party Transaction [Line Items]
Commitment to investment vehicle								$ 100
Investment vehicle					$ 350		$ 350		$ 350

[1] See Note 2 and 4 for a discussion of the methodology employed by the Company in calculating the subordinated income incentive fees.